Abo Bibliothek: Guest

ISSN Online: 2377-424X

International Heat Transfer Conference 12
August, 18-23, 2002, Grenoble, France

Numerical Simulation of Heat Transfer during Growth of Vapor Bubbles in Nucleate Boiling

Get access (open in a dialog) DOI: 10.1615/IHTC12.2350
6 pages

Abstrakt

With the aid of a recently developed model (e.g. (Mann, 2001)) heat transfer, bubble growth, and departure diameters of vapor bubbles at horizontal walls can be predicted for low and moderate heat fluxes. In this model the region around a single bubble is subdivided into three parts: a small, ring-shaped zone between solid wall and bubble, the so-called micro-region, the bubble contour, and its surrounding liquid, the so-called macro-region.
In this paper emphasis is laid on fluid flow and heat transfer in the macro-region, in order to improve the model. The flow pattern in the liquid around a vapor bubble is determined by the time-variable movement of the growing vapor bubble and also by buoyancy forces in the liquid. The governing equations for flow and temperature field are established and solved with the aid of a finite element method.
In a first approximation the initial and boundary conditions as well as bubble growth were taken from the microregion model. For the first growing vapor bubble at a specific location, the liquid initially is undisturbed and the temperature field linear. For subsequent bubbles different initial conditions, because of the mixing of the fluid due to convection induced by the rising bubbles, were considered.
This enabled us to determine the influence of the flow, mostly neglected before, on heat transfer in the macro-region and to estimate the error in heat transfer when pure heat conduction is assumed.
The results show the influence of fluid flow on the temperature field and thus on heat transfer in the macro-region. The main effects occur in the direct vicinity of the bubble, where fluid flow is strongest. Natural convection flow can mostly be neglected. The brief time period in which a bubble grows and the strong forced flow prevent a noticeable influence of natural convection.